We have used xlsx4j to produce a number of reports which all work fine when we compile our code using Java 6 but not when compiling with Java 7!
We use a number of unusual characters in our reports, and we use code like the following to add them where required (similar code is used for other characters):
public static CTRElt getDoubleAngleWithSpaces()
{
if (doubleAngleWithSpaces == null)
{
doubleAngleWithSpaces = new CTRElt();
Character dbleAngle = ...